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Download pdf 1.1MB - FAUNA Paraguay

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Robbins * PIPRA

Robbins * PIPRA FASCIICAUDA DISPLAYS 339 hibit the tail-up freeze, it seems likely that the twist of P. filicauda may have been derived from it. Upon isolation, selection may have favored male P. jilicauda that adopted movement during the tail-up freeze. Oc- casional contact between the male’s tail and the female during this display may have promoted the coevolution of the long tail filaments and the twist- ing motion in P. filicaudu (Schwartz and Snow 1978). Females of P. fus- ciicuudu occasionally hop quite close to a male performing the tail-up freeze, almost making contact with his tail and vent region. On four oc- casions, immature males of P. fusciicuudu pecked at the erected lower back feathers, tail and/or undertail coverts of an adult male during this display. Schwartz and Snow (1978) noted this same phenomenon exhibited by immature males of P. jilicaudu during the twist. Another notable plumage characteristic restricted to the P. uureolu complex is the presence of white in the flight feathers. This striking feature further enhances the conspicuousness of the displaying males. It is evident in all flight displays and aids in accenting the vent region during the tail- up freeze. Furthermore, the degree of coordination between displaying males of this complex is apparently unequaled by other Pipru and sur- passed in Pipridae only by Chiroxiphiu spp. The aerial chase is unreported for P. jilicuudu and P. uureolu; however, this relatively rare behavior may go undetected without prolonged study. The aerial chase and the butterfly display are very similar behaviors, with both incorporating the relatively slow, conspicuous wing beat. The precursor of these displays may have developed out of conflicts between two (or more) birds when one individual chased another around or from his territory. Competing males may have adopted the slower wing beat as a means of reducing the intensity of chases. Presumably, males were gradually acquiring more conspicuous plumage, e.g., increased white in the wings. With the gradual decrease in aggression between males, allowing for the evolution of joint display, the chase behavior may have been incorporated into the nonaggressive, highly-ritualized butterfly display, with its subsequent decrease in use in conflicts. This may explain why the aerial chase is relatively rare and occurs only when there is intense competition for a territory between three or more males. As with the aerial chase, the lack of observation of the horizontal freeze in the other two species may be an artefact of short term studies. This display may have evolved from the more generalized stationary displays, since in both displays the bird is horizontal (more so in the freeze) and anticipates the action of another bird (only females in the freeze). The swoop-in flights of P. jilicuudu and P. fusciicuudu differ in two notable ways. Whether in solo or joint display, male P. fusciicuudu ter- minate the swoop-in flight on the main perch. The only exception is during

340 THE WILSON BULLETIN - Vol. 95, No. 3, September 1983 duets when the passive partner fails to bend down and fly as the active bird approaches the perch. In such instances, the active male will either fly over the main perch or, less frequently, will land quietly next to the passive bird. This contrasts sharply with similar behavior of P. jilicauda, wherein usually, either in solo or duets, the performer over flies the main perch and lands on a nearby one (Schwartz and Snow 1978). In addition, male P. fasciicauda give only a single culminating call at the termination of a swoop-in flight. Schwartz and Snow (1978) identified two different, but quite similar, calls in P. jilicauda that are given under different cir- cumstances at the termination of the swoop-in flight. The first, and most frequently given, the pass-by call, is delivered by an active bird as it flies over the main perch and lands on an auxilliary perch. The second, some- what longer version, is given when the male flies over and then veers back to the main perch. Schwartz and Snow (1978) distinguished two types of soft, sweee, whis- tles of P. jilicauda. Shorter whistles (~0.4 set) were termed “conflict whistles,” while longer ones (>0.5 set) were referred to as “appeasement whistles.” I recorded both short and long as well as intermediate whistles for P. fasciicauda that are similar to those of P. filicauda. The whistle is more gradually inflected upward in P. fasciicauda. In P. fasciicauda there seemed to be little distinction in context between short and long whistles, since the same individual may intermix them. The duration of the advertisement call of P. fasciicauda is alost twice that of P. jilicauda. The “normal” and partial display calls are apparently nonexistent in P. jilicauda. However, a spectrogram in Schwartz and Snow’s (1978: Fig. 3K) paper is similar to that of the slurred display call of P. fasciicauda. Schwartz and Snow (1978) did not determine the func- tion of the call represented in the above spectrogram; however, since the call is apparently given under similar circumstances to that of P. fasci- icauda’s slurred display call, it probably serves the same function, i.e., to attract birds to display. One of the calls, a double-noted thee-weep, described by Snow (1963a) for P. aureola may be a homologue of the “normal” display call of P. fasciicauda. The display sites of P. fasciicauda and P. jilicauda apparently differ notably. However, caution must be exercised in comparing display sites until each species has been studied under a variety of situations. The understory in P. filicauda leks is apparently more open than that in P. fascicauda leks; in fact, Schwartz and Snow (1978:55) mention that the understory below 24 m at P. jilicauda leks is particulary bare, with only “a sparse to moderately dense scattering of sapplings and vines.” All display sites of P. fasciicauda (five different leks were visited) had dense vegetation below 2 m. Foliage density above 2 m varied from moderate to

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